Tagged toads reveal secrets to invasion success

By tagging 20 adult cane toads with acoustic fish tags the researchers have found the normally nocturnal toad is entering man-made dams to cool down and rehydrate during the day

Invasive, toxic and a major threat to Australia's native predators, the cane toad (Rhinella marina) has been a relentless coloniser of Australia's wet-dry tropics and is now conquering Australia's northern deserts.

Just how this normally tropical amphibian can survive the long, hot dry seasons in arid Australia has puzzled scientists, but UTS-led research has finally revealed this ugly amphibian's secret: the toad may be changing a key behaviour to survive harsh conditions, thereby improving its chances of ongoing success.

Using a novel approach, researchers led by UTS ecologist Jonathan Webb, have documented for the first time the normally nocturnal adult cane toad entering man-made dams to cool down and rehydrate during the day. This dramatic change in activity patterns allows toads to avoid the hostile daytime conditions faced on land.

Picture by Tim Dempster

By tagging 20 adult cane toads with acoustic fish tags and then placing data loggers in the dams near the Tanami desert – Australia's northernmost desert – the researchers were able to record the activity patterns of the toads. The 16mm long acoustic tags transmit through water, but not air, so the loggers only record the presence of a toad when they are sitting or swimming in water.

"No-one has ever put fish tags on amphibians before to study their activity and what we found shows amazing behavioural flexibility on the part of these toads," Dr Webb said.

"We found that cane toads visit the water during the day time, with peaks of activity in the morning. This is very different to what toads do in their native geographic range and the rest of Australia – usually adult toads are strictly nocturnal. This daytime hydrating and cooling down allows them to survive an environment where ground temperatures often exceed 40 degrees for several hours each day," he said.

The team, which includes conservation scientists from UNSW and the University of Melbourne, believes that such behavioural flexibility, or "plasticity", may explain why cane toads are one of the world's most successful invasive species. That's more bad news for already environmentally stressed populations of native predators such as quolls and goannas.

"Plasticity, or evolution in behavioural responses, is a key attribute of successful animal invasions," Dr Webb said. "The behavioural phase shift that this research has revealed has rarely been reported in invasive species and could facilitate ongoing invasion success for the cane toad."

The research is being published today in the Royal Society journal Biology Letters and was funded by The Hermon Slade Foundation and the Australian Research Council.